Photosensor for a transmitted light method used for detecting the direction of movement of intensity maxima and intensity minima of an optical standing wave

ABSTRACT

A photosensor for a transmitted-light method for detecting the intensity profile of an optical standing wave, with a transparent substrate, with a semiconductor component, and with at least three contacts, is characterized by the fact that two semiconductor components are connected with each other, such that the first semiconductor component and the second semiconductor component each have a photoelectrically active first semiconductor layer, and such that the two photoelectrically active semiconductor layers have a fixed phase relation to each other, which is adjusted by at least one photoelectrically inactive layer.

[0001] The invention concerns a photosensor for a transmitted-lightmethod for detecting the direction of movement of the intensity maximaand intensity minima in an intensity profile, with a transparentsubstrate, two first semiconductor components assigned to the substrate,and at least three contacts.

[0002] In the field of photoelectric detection of visual radiation,photosensors that operate by a wide variety of principles are used,e.g., as photoresistors, photodiodes, phototransistors, or the like. Acommon feature of all of these designs is that the visual radiation isdetected by the incident-light method. Typical applications for thesetypes of photosensors are, e.g., light barriers or monitoring andsecurity systems.

[0003] Another very specific area of application of photoelectricdetection is optical interferometers. A typical example and one which isoften used for technical length measurements is the Michelsoninterferometer, in which a beam splitter splits a light beam into twosplit beams, which then follow different paths and, after beingreflected back to the beam splitter plate, are recombined at the plate.In accordance with the state of the art, two signals with a mutual phaseshift of 90° are photoelectrically derived from the differentialstructure produced at the interferometer exit to detect the direction ofmovement of the measuring mirror. As in the case of all of the otherphotoelectric applications mentioned above, the detection of theradiation also occurs in incident light.

[0004] By contrast, when an optical standing wave forms, the two beamsthat produce the interference propagate in opposite directions. For thisreason, the technical utilization and photoelectric evaluation of theresult of the interference of an optical standing wave can be carriedout only in transmitted light.

[0005] DE 33 00 369 and U.S. Pat. No. 4,443,107 describe designs for astanding-wave interferometer. In line with the requirements oninterferometers for the automatic detection of the direction of movementof the measuring mirror, two photosensors are provided in each case,which generate two signals with a mutual phase shift of 90° fordetecting the direction of movement of the measuring mirror. Thephotosensors are applied to a glass substrate, whose thickness must befinished with a precision of a few nanometers by the methods of opticalprecision finishing to maintain the 90° phase shift as precisely aspossible. This requires the application of considerable technologicalresources, which is associated with high costs.

[0006] DE 36 12 221 describes placing a piezoelectrically activecomponent between the two photosensors and making the distance betweenthe sensors adjustable. Although this solution significantly reduces theexpenditure of technological resources, it is still necessary, e.g., inthe event of temperature changes, to detect any changes in the distancebetween the sensors and to adjust the distance.

[0007] Therefore, the objective of the present invention is to realize aphotosensor, in which the adjustment of the phase position between twophotosensors is inexpensively integrated in the semiconductor productionprocess sequence and therefore can be carried out with a high degree ofprecision, such that the effect on the phase position by outsideinfluences, e.g., changes in the ambient temperature, is reduced to anirrelevant magnitude.

[0008] This objective is achieved by the characterizing features ofclaim 1.

[0009] The arrangement of at least two semiconductor components togetheron a substrate eliminates the expensive adjustment of the transparentphotosensors. With two transparent photosensors produced on a commontransparent substrate, a certain number 1 of essentially transparentlayers with different functions are situated between thephotoelectrically active layers of the two transparent photosensors.

[0010] If an optical standing wave is now produced by means of a laserand a plane mirror, and this substrate with the two transparentphotosensors is arranged on the optical axis of the standing wave insuch a way that the transparent photosensors are arranged one behind theother along the optical axis, the standing wave propagates through thesubstrate, the two transparent photosensors, and the functional layers.Starting from the photoelectrically active layer of the transparentphotosensors, the following is obtained as the corresponding period:modified$p = {\frac{1}{\lambda} \cdot {\sum\limits_{j = 1}^{l}{d_{j}n_{j}}}}$

[0011] where λ is the wavelength of the coherent radiation that is used,1 is the number of semiconductor layers between the photoelectricallyactive layers, d is the layer thickness, and n is the index ofrefraction of the essentially photoelectrically inactive layer. If theperiod p is adjusted in such a way that it satisfies the conditionmodified${p = {\frac{k}{8} - \frac{d_{s1}n_{s1}}{2\lambda} - \frac{d_{s2}n_{s2}}{2\lambda}}},$

[0012] where k=1, 3, 5, . . . then, if the plane mirror is displaced,there is a mutual phase shift of 90° or an odd multiple of 90° betweenthe photoelectric signals produced by the photoelectrically activelayers of the transparent photosensors.

[0013] A common feature of the transparent photosensors is that theyproduce a photocurrent as a function of the intensity profile in astanding wave. In this regard, an optimal detection condition for thephotocurrent is that the layer thickness of the photoelectrically activelayer of the transparent photosensor is$d \leq \frac{\lambda}{4 \cdot n}$

[0014] where λ is the wavelength and n is the index of refraction of thephotoelectrically active layer.

[0015] Further advantages are apparent from the features of dependentclaims 4 to 15.

[0016] An embodiment of the present invention is described in greaterdetail below with reference to the drawings.

[0017]FIG. 1 shows a schematic diagram of the passage of a standing wavethrough a photosensor of the invention.

[0018]FIG. 2 shows a schematic cross-sectional view of the photosensorof the invention, in which a photocurrent flows parallel to thedirection of propagation of the standing wave.

[0019]FIG. 3 shows a schematic view of the photosensor of the invention,in which a photocurrent flows perpendicularly to the direction ofpropagation of the standing wave.

[0020]FIG. 1 shows a schematic diagram of the passage of a standing wavethrough a photosensor of the invention. The layer thickness of thephotoelectrically active layers d_(s1) and d_(s2) is $\begin{matrix}{d_{s1} \leq \frac{\lambda}{4\quad n_{s1}}} & {{Equation}\quad 1} \\{d_{s2} \leq \frac{\lambda}{4n_{s2}}} & {{Equation}\quad 2}\end{matrix}$

[0021] where n_(s1) and n_(s2) are the indices of refraction of thephotoactive layers d_(s1) and d_(s2). In general, the phase conditionmay be described as modified $\begin{matrix}{{\sum\limits_{j = 1}^{l}{n_{j}d_{j}}} = {{k\frac{\lambda}{8}} - \frac{d_{s1}n_{s1}}{2} - \frac{d_{s2}n_{s2}}{2}}} & {{Equation}\quad 3}\end{matrix}$

[0022]FIG. 2 shows a cross section of a photosensor 1 of the invention,to which the diagram of FIG. 1 is to be applied. The photosensor 1 isarranged between a radiation source 3 and a mirror 5. This arrangementis set up in such a way that the optical axis of a standing wave 4produced by the radiation source 3 passes perpendicularly through thethickness of the photosensor 1 and is perpendicularly incident on themirror. The photosensor 1 comprises a substrate 7, which may be composedof glass, quartz, or plastic. If a plastic substrate is selected, it maybe formed especially as a plastic film. In the present embodiment, aseries of semiconductor components 9, 11 (partial sensors 1 and 2) isformed on the mirror side of the substrate 7, i.e., on the side of thesubstrate 7 facing away from the radiation source 3. However, this isnot necessarily the case in other embodiments. The substrate 7 and eachsemiconductor component 9 and 11 are essentially transparent in such away that the standing wave 4 of the radiation source 3 can pass throughthe photosensor 1 to the mirror 5. A photocurrent is generated in eachsemiconductor component 9, 11 as a function of the intensity profile ofthe standing wave 4 by reflection of the standing wave 4 at the mirror5.

[0023] The semiconductor component 9 applied on the substrate 7comprises, in the following order, starting from the substrate 7, atransparent contact layer 9.1, a transparent first n-doped semiconductorlayer 9.2, an intrinsic second semiconductor layer 9.3, an n-doped thirdsemiconductor layer 9.4, and a second transparent contact layer 9.5. Thesecond semiconductor component 11 comprises, in the following order,starting from the second contact layer 9.5, a transparent first n-dopedsemiconductor layer 11.2, an intrinsic second semiconductor layer 11.3,an n-doped third semiconductor layer 11.4, and a third transparentcontact layer 11.5. The contact layers 9.1, 9.5, and 11.5, and the twosets of first, second, and third semiconductor layers 9.2, 9.3, 9.4, and11.2, 11.3, 11.4, respectively, are arranged in a plane-parallel fashionin the semiconductor components 9 and 11, respectively, each borderingon the next in order, and perpendicularly to the optical axis of thestanding wave 4. The intrinsic second semiconductor layers 9.3 and 11.3have layer thicknesses d parallel to the direction of propagation of thestanding wave 4 of d_(s1)≦λ/4n_(s1) and d_(s2)≦λ/4n_(s2), where λ is thewavelength of the optical coherent wave that is used, n₁ is the index ofrefraction of the photoelectrically active second semiconductor layer9.3, and n₂ is the index of refraction of the photoelectrically activesecond semiconductor layer 11.3. The n_(n2)-doped semiconductor layers9.2, 9.4, 11.2, and 11.4 are essentially photoelectrically inactive.

[0024] The fixed phase relation between electrically activesemiconductor layers 9.3, 11.4 of the transparent photosensor 1 can beeffected by means of at least one photoelectrically inactivesemiconductor layer 9.2, 9.4, 11.1, 11.4 composed of amorphous,nanocrystalline, microcrystalline, polycrystalline, or crystallinesilicon, germanium, carbon, nitrogen, oxygen, or alloys of thesematerials, or it may be produced from a transparent conductive oxide,e.g., SnO₂, Z_(n)O, In₂O₃, or Cd₂SnO₄, which is doped with B, Al, In,Sn, Sb, or F. The choice of the semiconductor layer or semiconductorlayers 9.2, 9.4, 11.1, 11.3, with which the phase relation is adjusted,depends on the choice of the transparent photosensor 1. The substrate 7is produced from a material, which may be, e.g., a glass substrate, aquartz substrate, or a substrate made of plastic, especially a plasticfilm.

[0025] In the photosensor 1 in FIG. 2, the photocurrent flows parallelto the direction of propagation of the standing wave 4. nin-Structures,for example, are used as transparent semiconductor layers 9.2, 9.3, 9.4and 11.1, 11.2, 11.3, but other well-known structures are alsoconceivable. The phase relation between the two semiconductor components9 and 11 is adjusted for the second contact layer 9.5 (TCO layer), whichsimultaneously serves as the common contact for the two semiconductorcomponents 9 and 11. To determine the layer thickness of the TCO layer(90° phase relation between the electrical signals), it is necessary toconsider the effect of the two half, photoelectrically active,semiconductor layers 9.3 and 11.2 and of the two doped semiconductorlayers 9.4 and 11.1, which border on the middle, second, transparentcontact surface 9.5.

[0026] Alternatively, it is also possible to realize a structure inwhich the photocurrent flows perpendicularly to the direction ofpropagation of the standing wave 4. A photosensor 1 of this type isshown in FIG. 3. In this case, for example, the photoconductivity of anamorphous semiconductor layer is used as the transparent photosensor 1.The contact layers consist, for example, of aluminum coatings applied byvapor deposition. In this design, it is not necessary for the contactlayers to be transparent. To achieve better contact, doped regions maybe introduced or applied below the metal contacts. In this case, thephase relation can be adjusted by an insulating layer 13 applied betweenthe two semiconductor components 9, 11. For example, a silicon nitritelayer is indicated in FIG. 3. This layer insulates the two semiconductorcomponents 9, 11 from each other and provides for a phase relation of90°. A second insulating layer 15, likewise in the form of a siliconnitrite layer, is applied to the semiconductor component 11 and isdesigned to improve the optical adaptation of the layered system to theconditions of the standing wave. The use of these additionalsemiconductor layers makes it possible to optimize the layered structurewith respect to minimum reflection and maximum transmission.

[0027] For several reasons, especially amorphous, nanocrystalline,microcrystalline, and crystalline silicon and its alloys are suitablefor the realization of a semiconductor sensor. For example, amorphousand microcrystalline silicon can be produced on various materials, suchas glass, quartz, or plastic film, in a low-temperature process(deposition temperature 200-300° C.) by plasma-enhanced chemical vapordeposition (PECVD). In this regard, the transparent and conductivelayers are used as contact layers. Due to the possibility of depositingthin amorphous and microcrystalline layers on transparent substrates atlow temperatures, these layers are very well suited as absorbermaterials for a semiconductor sensor in transmitted-light operation.Thus, it is possible to produce very thin layered systems by systematiccontrol of the process parameters during production.

[0028] The transparent and electrically conductive layers (TCO layers)can be produced, for example, by a CVD process, spray pyrolysis,vaporization process, and sputtering process. Like the PECVD process,this process is also a low-temperature process.

[0029]FIG. 1. Intensität [a. E.]=intensity, arbitrary units

[0030]FIG. 2. Substrat=substrate

[0031]FIG. 3. Metallisierung=metallization; Substrat=substrate

1. Photosensor for a transmitted-light method for detecting a directionof movement of the intensity maxima and intensity minima in an intensityprofile, with an optical standing wave, with a transparent substrate(7), with two essentially transparent semiconductor components (9, 11),and with at least one contact layer (9.5) or insulating layer (13),wherein the first semiconductor component (9) is connected with thesecond semiconductor component (11) by the contact layer (9.5) orinsulating layer (13), characterized by the fact that the firstsemiconductor component (9) has a first transparent photoelectricallyinactive semiconductor layer (9.2, 9.4) and a first transparentphotoelectrically active semiconductor layer (9.3), the secondsemiconductor layer (11) comprises a first transparent photoelectricallyinactive semiconductor layer (11.2, 11.4) and a second transparentphotoelectrically active semiconductor layer (11.3), and the twosemiconductor components (9, 11) have a fixed phase relation to eachother, wherein the first photoelectrically active semiconductor layers(9.3) of the first semiconductor component (9) has a layer thicknessd_(s1) parallel to the direction of propagation of the standing wave (4)of d_(s1)≦λ/4n_(s1), and the second photoelectrically activesemiconductor layers (11.3) of the second semiconductor component (11)has a layer thickness d_(s2) parallel to the direction of propagation ofthe standing wave (4) of d_(s2)≦λ/4n_(s2), wherein λ is the wavelengthof the optical coherent wave, and n_(s1) and n_(s2) are the indices ofrefraction of the photoelectrically active first and secondsemiconductor layers (9.3, 11.2)
 2. Photosensor in accordance with claim1, characterized by the fact that the fixed phase relation is${{k\frac{\lambda}{4}} = {{\sum\limits_{j = 1}^{l}{d_{j}n_{j}}} + \frac{d_{s1}n_{s1}}{2} + \frac{d_{s2}n_{s2}}{2}}},$

wherein k is an odd whole number, λ is the wavelength of the coherentradiation that is used, 1 is the number of semiconductor layers usedbetween the active semiconductor layers of the semiconductor components1 and 2 (9; 11), d_(s1) is the layer thickness of the photoelectricallyactive first semiconductor layers (9.3), d_(s2) is the layer thicknessof the photoelectrically active second semiconductor layer (11.2), d₁ .. . d₁ are the layer thicknesses of the photoelectrically inactivesecond semiconductor layers, n₁ . . . n₁ are the indices of refractionof the essentially photoelectrically inactive first semiconductor layers(9.2, 9.4; 11.1, 11.3), n_(s1) is the index of refraction of thephotoelectrically active first semiconductor layer, and n_(s2) is theindex of refraction of the photoelectrically active second semiconductorlayer.
 3. Photosensor in accordance with claim 1 or claim 2,characterized by the fact that the semiconductor components are realizedas photoconductors, as Schottky barrier diodes, or as pin, nip, pip,nin, npin, pnip, pinp, or nipn structures, or combinations of thesestructures, wherein the charge transfer within the transparentphotosensors may occur both parallel to and perpendicularly to thedirection of propagation of the standing wave.
 4. Photosensor inaccordance with any of the preceding claims, characterized by the factthat the transparent substrate (7), on which the first semiconductorcomponent (9) is applied, is transparent to the coherent radiation ofwavelength λ.
 5. Photosensor in accordance with any of claims 1 to 4,characterized by the fact that at least one of the semiconductor layers(9.2, 9.3, 9.4; 11.1, 11.2, 11.3) is composed of a material selectedfrom the group comprising amorphous material, microcrystalline material,polycrystalline material, and crystalline material.
 6. Photosensor inaccordance with any of claims 1 to 5, characterized by the fact that atleast one of the semiconductor layers (9.2, 9.3, 9.4; 11.1, 11.2, 11.3)is composed of a material selected from the group comprising silicon,germanium, carbon, oxygen, nitrogen, an alloy of these materials,transparent conductive oxides, and thin metal films.
 7. Photosensor inaccordance with any of the preceding claims, characterized by the factthat the transparent substrate (7) is composed of a material selectedfrom the group comprising glass, quartz, and plastic film. 8.Photosensor in accordance with any of the preceding claims,characterized by the fact that each contact layer (9.1; 9.5; 11.4) iscomposed of a material selected from the group comprising NO₂, ZnO,In₂O₃, and Cd₂SnO₄, which are doped with an element from the groupcomprising B, Al, In, Sn, Sb, and F, thin metal films, andsemiconducting layers.
 9. Photosensor in accordance with any of thepreceding claims, characterized by the fact that a layer is formed oneach semiconductor component (9) for the optical adaptation of thesemiconductor component.
 10. Photosensor in accordance with any of thepreceding claims, characterized by the fact that the photosensor isdesigned as a one-dimensional or two-dimensional sensor field.